1. Field of the Invention
The present invention relates generally to deaerators used in combined cycle power plants, and more particularly to methods and apparatus improving the efficiency of those combined cycle power plants by providing means for heating condensate supplied to such deaerators with feedwater that is deaerated thereby.
2. Statement of the Prior Art
It is well known within the field of power generation to provide one or more combustion turbines in a plant with one or more steam turbines, wherein the waste heat that is exhausted by the combustion turbine(s) is used to generate motive steam for the steam turbine(s) and all turbines are coupled to generators to produce electrical power. Plants such as these are typically referred to as "combined cycle power plants".
As with conventional combined cycle power plants, the steam turbines used therein include an inlet portion which receives the motive steam generated by the waste heat from the combustion turbines, as well as an exhaust portion for exhausting the spent motive steam from the steam turbines. A condenser that is connected to the exhaust portion of the steam turbine receives the spent motive steam and condenses same to provide a supply of condensate.
The combustion turbines (which are also referred to as "gas" turbines) each include an exhaust portion to exhaust the waste heat that they produce in the form of gases to a heat recovery steam generator or "HRSG". Such HRSG's are connected between the exhaust portion of the gas turbine(s) and the inlet portion of the steam turbine(s) for receiving the waste heat that is exhausted by the gas turbine(s), for generating the motive steam from a supply of feedwater that is heated by such waste heat, and for supplying the motive steam to the steam turbine(s). A conventional deaerator is connected to the condenser to receive therefrom the supply of condensate and for deaerating such condensate to provide the supply of feedwater to the HRSG.
In typical combined cycle power plants, the supply of feedwater for the HRSG's is provided by boiler feed pumps which receive relatively warm (e.g., from about 220.degree. F.-250.degree. F.), deaerated water from the deaerator. Additional heat could be recovered from the exhaust gases in the HRSG by the mere provision of a supply of feedwater that is relatively cool, for example, by providing the condensate directly from the condenser to the HRSG. The additional heat which would be recovered in this manner would increase overall efficiency of the combined cycle power plant, but would concomitantly necessitate the usage of expensive, corrosion-resistant materials for all of the heat transfer surfaces in the HRSG since such HRSG would be required to operate with feedwater which is not deaerated.